WO2003045900A1

WO2003045900A1 - Production of isocyanates in the gaseous phase

Info

Publication number: WO2003045900A1
Application number: PCT/EP2002/012930
Authority: WO
Inventors: Andreas Wölfert; Christian Müller; Eckhard Ströfer; Joachim Pfeffinger; Markus Weber; Carsten KNÖSCHE
Original assignee: Basf Aktiengesellschaft
Priority date: 2001-11-28
Filing date: 2002-11-19
Publication date: 2003-06-05
Also published as: US7084297B2; EP1451150A1; DE50214172D1; ATE455094T1; ES2338537T3; EP1451150B1; JP4167177B2; KR20040058335A; KR100885224B1; US20050070734A1; AU2002360937A1; CN1592736A; DE10158160A1; CN1266123C; JP2005510558A

Abstract

The invention relates to a method for producing isocyanates by reacting primary amines with phosgene in the gaseous phase. Said method is characterized in that the reaction of amine and phosgene occurs in a reaction channel, the internal dimensions of which have a width/height ratio of at least 2/1.

Description

Production of isocyanates in the gas phase

description

The invention relates to a process for the preparation of isocyanates by reacting primary amines with phosgene in the gas phase, characterized in that the reaction of amine and phosgene takes place in a reaction channel, preferably a plate reactor, the internal dimensions of the reaction channel being a ratio from width to height of at least 2: 1.

Various processes for producing isocyanates by reacting amines with phosgene in the gas phase are known from the prior art. EP-A-593 334 describes a process for the preparation of aromatic diisocyanates in the gas phase, characterized in that the reaction of the diamine with phosgene takes place in a tubular reactor without moving parts and with a narrowing of the walls along the longitudinal axis of the tubular reactor. The process is problematic, however, because the mixing of the educt streams alone works poorly by narrowing the tube wall compared to using a correct mixing element. Poor mixing usually leads to an undesirably high formation of solids.

EP-A-699 657 describes a process for the preparation of aromatic diisocyanates in the gas phase, characterized in that the reaction of the associated diamine with the phosgene takes place in a two-zone reactor, the first zone containing 20% to 80% of the Total reactor volume, is ideally mixed and the second zone, which makes up 80% to 20% of the total reactor volume, can be characterized by a piston flow. However, because at least 20% of the reaction volume is ideally back-mixed, an uneven residence time distribution results, which can lead to an undesirably increased formation of solids.

EP-A-289 840 describes the production of diisocyanates by gas phase phosgenation, the production taking place according to the invention in a turbulent flow at temperatures between 200 ° C and 600 ° C in a cylindrical space without moving parts. By avoiding moving parts, the risk of phosgene leakage is reduced. Due to the turbulent flow in the cylindrical space (tube), apart from fluid elements near the wall, a relatively good uniform flow distribution in the tube and thus a relatively narrow residence time distribution is achieved, which, as described in EP-A-570 799, can lead to a reduction in solid formation.

EP-A-570 799 relates to a process for the preparation of aromatic diisocyanates in the gas phase, characterized in that the reaction of the associated diamine with the phosgene is carried out in a tubular reactor above the boiling point of the diamine within an average contact time of 0.5 to 5 seconds becomes. As described in the document, too long and too short reaction times lead to undesirable solid formation. A method is therefore disclosed in which the mean deviation from the mean contact time is less than 6%. Adherence to this contact time is achieved by carrying out the reaction in a tube flow which is characterized either by a Reynolds number above 4,000 or a Bodenstein number above 100.

EP-A-749 958 describes a process for the preparation of triisocyanates by gas phase phosgenation of (cyclo) aliphatic triamines with three primary amino groups, characterized in that the triamine and the phosgene are heated continuously in a to 200 ° C. to 600 ° C. , cylindrical reaction chamber with a flow rate of at least 3 m / s to react with each other.

EP-A-928785 describes the use of microstructure mixers for phosgenation of amines in the gas phase. A disadvantage of using micromixers is that even the smallest amounts of solids, the formation of which cannot be completely ruled out in the synthesis of the isocyanates, can lead to clogging of the mixer, which reduces the time availability of the phosgenation plant.

For the production of isocyanates on an industrial scale, there are two possibilities for technical implementation in the known gas phase phosgenation processes which use a cylindrical reaction space. On the one hand, the reaction can be carried out in a single pipe section, the diameter of which has to be adapted to the production capacity of the plant. For very large production plants, this concept has the disadvantage that an exact temperature control of the reaction streams (phosgene and amine) in the core of the flow can no longer be achieved by wall heating the tube. However, local temperature inhomogeneities can lead to product decomposition at too high a temperature or inadequate conversion of the starting materials to the desired isocyanate at too low a temperature. The second possibility of technical implementation is the division of the reacting mixture into individual partial streams, which are then passed in parallel through smaller, individual pipes, which can be better tempered due to their smaller diameter. A disadvantage of this method variant is that this variant is relatively susceptible to blockage if the volume flow through each individual tube is not regulated. If, for example, one of the pipes gets deposits at one point, the pressure loss of the flow through this pipe is greater. The reaction gas therefore automatically switches to the other tubes. There is less flow through the tube with the deposits. If, however, the flow in the pipe beginning to become blocked becomes less, the flow in this pipe has an extended dwell time, which, as already explained in EP 570 799, leads to an increase in the formation of solid matter. In addition, any solids from a slow flow can settle much more easily on the pipe wall, which speeds up clogging.

In summary, in large-scale gas phase phosgenation, the use of a large tube has the problem of tempering the overall flow and the use of many small tubes has the risk of uneven flow. Both problem areas lead to an uneven progress of the reaction and thus to solids, which reduces the operability of the system.

The object of the invention is therefore to provide a process for the preparation of isocyanates by phosgenation in the gas phase, both a high heat exchange area and, despite solid formation which cannot be completely prevented, the longest possible operating time of the production plants, in particular of a large-scale production plant, being achieved.

Surprisingly, it was found that the continuous phosgenation of amines in the gas phase is advantageous, i.e. For example, with a significantly increased number of operating hours of the production plant, if the reaction is carried out in a non-cylindrical reaction channel, preferably a plate reactor, which preferably has a height which enables advantageous temperature control of the reactants and which has a width which is at least that is twice the height.

The invention therefore relates to a process for the preparation of isocyanates by reacting primary amines with phosgene in the gas phase, characterized in that the reaction of amine and phosgene takes place in a reaction channel, where the internal dimensions of the reaction channel have a ratio of width to height of at least 2: 1.

The invention furthermore relates to the use of a plate reactor, the internal dimensions of the plate reactor being one

Have a ratio of width to height of at least 2: 1 for the production of isocyanates by reacting primary amines with phosgene in the gas phase.

Finally, the invention relates to the use of a reactor block containing at least two of the plate reactors described above for the production of isocyanates by reacting primary amines with phosgene in the gas phase.

The reaction channel used in the present invention generally consists of a material that is essentially inert to the phosgenation reaction. Furthermore, it should generally withstand pressures of up to 10 bar, preferably up to 20 bar. Suitable materials are e.g. Metals such as steel, silver or copper, glass, ceramics or homogeneous or heterogeneous mixtures thereof. Steel reactors are preferably used.

The reaction channel used is preferably essentially cuboid. The reaction channel used has a width to height ratio of at least 2: 1, preferably at least 3: 1, particularly preferably at least 5: 1 and in particular at least 10: 1. The upper limit of the ratio of width to height depends on the desired capacity of the reaction channel and is in principle not limited. Reaction channels with a ratio of width to height up to a maximum of 5000: 1, preferably 1000: 1, have proven technically useful.

The height of the reaction channel is generally not limited. For example, it is possible to carry out the reaction in a high reaction channel with a height of, for example, 40 cm. If, however, a better heat exchange is to take place with the reactor walls, the reaction can be carried out in reaction channels of low height, for example only a few centimeters or millimeters.

In general, the reaction channel has a height of 1 millimeter to 50 centimeters, preferably from 2 millimeters to 20 centimeters, particularly preferably from 3 millimeters to 3 centimeters. The length of the reaction channel depends on the desired degree of conversion of the reaction and is generally ten times the height of the reaction channel, preferably twenty times, in particular fifty times the height of the reaction channel. The length of the reactor preferably does not exceed 10,000 times, particularly preferably not 5,000 times, in particular not 4,000 times, the height of the reaction channel.

In a preferred embodiment, the length of the reaction channel is at least 1 meter, usually 2 to 50 meters, preferably 5 to 25 meters, particularly preferably 10 to 20 meters.

The reaction channel used is preferably essentially cuboid. Depending on the technical design, however, it can have rounded corners and / or edges. Likewise, the surfaces forming the cuboid cannot be flat but curved. Unless the height, width or length is the same at all points in the cuboid, the values for the internal dimensions of the reaction channel disclosed in the description and in the claims relate to the average (i.e. average) height, average width or average length. Figures 1 to 8 in Figure 1 show possible embodiments of the reaction channel.

The walls of the reaction channel can be smooth or profiled. For example, cracks or waves are suitable as profiles.

The reaction channel used in the present invention is preferably a plate reactor. This is preferably constructed from plate-shaped layers. Rectangular, plate-shaped layers are particularly preferably used. In general, the plate reactor can be composed of four rectangular, plate-shaped materials, so that the plate reactor preferably has the shape of a cuboid. The edges of such a cuboid can have an angle of approximately 90 °, but they can, however, also be rounded.

It is also possible to assemble the plate reactor from two plate-shaped layers with at least one edge bent up to approximately 90 °, so that a cuboid reaction channel is formed.

In a preferred embodiment, the reaction channel at the inlet opening contains a distribution element, the distribution element containing suitable deflection elements which distribute the gas stream as homogeneously as possible essentially over the entire width of the reaction channel. The deflection elements mentioned can consist, for example, of bent metal sheets. The reaction components amine and phosgene can be mixed before or in the reaction channel. It is thus possible to connect a mixing unit, for example a nozzle, upstream of the reaction channel, as a result of which a mixed gas stream containing phosgene and amine already enters the reaction channel.

In a preferred embodiment, the phosgene stream is first distributed as homogeneously as possible over the entire width of the reaction channel by means of a distribution element. The amine stream is supplied at the beginning of the reaction channel, here a distributor channel with holes or mixing nozzles is introduced in the reaction channel, this distributor channel preferably extending over the entire width of the reaction channel. The amine, which is optionally mixed with an inert medium, is fed to the phosgene stream from the holes or mixing nozzles.

The inert medium is a medium which is gaseous at the reaction temperature and does not react with the starting materials. For example, nitrogen, noble gases such as helium or argon or aromatics such as chlorobenzene, dichlorobenzene or

Xylene can be used. Nitrogen is preferably used as the inert medium.

Primary amines can be used for the process according to the invention, which can preferably be converted into the gas phase without decomposition. Amines, in particular diamines, based on aliphatic or cycloaliphatic hydrocarbons having 1 to 15 carbon atoms are particularly suitable here. Examples include 1, 6-di-minohexane, 1-amino-3, 3, 5-trimethyl-5-amino-ethy1cyc1ohexane (IPDA) and 4, 4'-diaminodicycloohexylmethane. 1,6-Diaminohexane (HDA) is preferably used.

Aromatic amines, which can preferably be converted into the gas phase without decomposition, can also be used for the process according to the invention. Examples of preferred aromatic amines are toluenediamine (TDA), as the 2,4- or 2,6-isomer or as a mixture thereof, diaminobenzene, naphthyldiamine (NDA) and 2,4'- or 4,4'-methylene (diphenylamine) ( MDA) or mixtures of isomers thereof.

In the process according to the invention, it is advantageous to use excess phosgene with respect to amino groups. A molar ratio of phosgene to amino groups is usually from 1.1: 1 to 20: 1, preferably from 1.2: 1 to 5: 1. To carry out the process according to the invention it can be advantageous to preheat the streams of the reactants before mixing, usually to temperatures from 100 to 600 ° C., preferably from 200 to 500 ° C. The reaction in the reaction channel usually takes place at a temperature of 150 to 600 ° C, preferably from 250 to 500 ° C. The process according to the invention is preferably carried out continuously.

In a preferred embodiment, the dimensions of the reaction channel and the flow velocities are dimensioned such that a turbulent flow, i.e. there is a flow with a Reynolds number of at least 2300, preferably at least 2700, the Reynolds number being formed with the hydraulic diameter of the reaction channel. The gaseous reactants preferably pass through the reaction channel at a flow rate of 20 to 150 meters / second, preferably 30 to 100 meters / second.

In general, the average contact time in the process according to the invention is 0.05 to 5 seconds, preferably 0.06 to 1, particularly preferably 0.1 to 0.45 seconds. The mean contact time is understood to mean the time period from the start of the mixing of the starting materials to the washing out of the reaction gas after leaving the reaction channel in the work-up stage. In a preferred embodiment, the flow in the process according to the invention is characterized by a Bodenstein number of more than 10, preferably more than 100 and particularly preferably more than 500.

A preferred embodiment of the method according to the invention is illustrated schematically in FIG. 2.

In Figure 2:

I amine template

II Phosgene template III Mixing unit IV Reaction channel V Processing stage VI Cleaning stage

1 solvent supply

2 Amine feed

3 Inert medium supply

4 Phosgene supply 5 Discharge of hydrogen chloride, phosgene and / or inert medium

6 Solvent discharge

7 discharge of isocyanate In the amine receiver, the amine, optionally together with an inert medium as carrier gas, such as nitrogen, is converted into the gas phase and fed into the mixing unit. Phosgene from the phosgene charge is also transferred to the mixing unit. After mixing in the mixing unit, which can consist, for example, of a nozzle or a static mixer, the gaseous mixture of phosgene, amine and, if appropriate, inert medium is transferred into the reaction channel. As illustrated in FIG. 2, the mixing unit does not have to be an independent reaction stage, rather it can be advantageous to integrate the mixing unit into the reaction channel. A preferred embodiment of an integrated unit comprising a mixing unit and reaction channel is shown in FIG. 3.

After the reaction mixture has been reacted in the reaction channel, it reaches the work-up stage. This is preferably a so-called washing tower, the isocyanate formed being separated from the gaseous mixture by condensation in an inert solvent, while excess phosgene, hydrogen chloride and, if appropriate, the inert medium pass through the work-up stage in gaseous form. Aromatic hydrocarbons which are optionally substituted with halogen atoms, such as chlorobenzene, dichlorobenzene and toluene, are preferred as inert solvents. The temperature of the inert solvent is particularly preferably kept above the decomposition temperature of the carbamoyl chloride belonging to the amine.

In the subsequent purification stage, the isocyanate is separated from the solvent, preferably by distillation. The removal of residual impurities, including hydrogen chloride, inert medium and / or phosgene, can also be carried out here.

Figure 3 illustrates a preferred embodiment of a

Reaction channel. In this embodiment, the reaction channel consists of a plate reactor which contains a distribution element and a collecting element at the two outlet openings. In Figure 3:

1 supply of phosgene stream

2 distribution element 3 deflection elements

4 distribution channel with outlet openings for amine

5 amine supply

6 plate reactor

7 collecting element 8 outlet channel

9 outlet openings for amine

The gaseous phosgene stream used is distributed as homogeneously as possible over the entire width of the plate reactor by means of a distribution element. For this purpose, deflection elements can be used, which can consist, for example, of angled metal sheets. The addition of the A ins takes place via a distributor channel, which preferably extends over the entire width of the plate reactor and is preferably arranged in close proximity to the distributor element. The distribution channel is preferably arranged at a medium height in the plate reactor and contains holes or mixing nozzles through which the amine stream is fed to the plate reactor and thus mixed with the phosgene stream. At the other end of the plate reactor, the gas stream is preferably focused in a collecting element and then fed to the processing stage.

The inert solvent for washing out the isocyanate can be added in the washing tower and / or already in the outlet region of the plate reactor 6 and / or between the plate reactor 6 and the collecting element 7 and / or in the collecting element 7 and / or in the outlet channel 8. An advantageous embodiment is characterized in that the reaction gases from the reaction channel are brought into contact with the inert solvent after the same dwell time in the reaction channel, if possible. In a preferred embodiment, the inert solvent is brought into contact with the reaction gas by means of nozzles which are fitted at the locations mentioned above.

In a preferred embodiment, the process according to the invention is carried out in a reactor block, the reactor block containing two or more, preferably 2 to 20, reaction channels described above, preferably plate reactors. The reaction channels can be arranged anywhere within the reactor block, they are preferably arranged one above the other. A suitable dimensioned tube, for example, is suitable as the reactor block, in the interior of which two or more reaction channels are arranged. The conversion of phosgene to amine takes place as follows was only in the reaction channels according to the invention, not in the reactor block. The reactor block merely serves as a kind of jacket for the reaction channels.

In a particularly preferred embodiment, the reactor block also contains, in addition to the reaction channels, a fluid which can flow between the individual reaction channels. This fluid is used for heat dissipation, i.e. for temperature control within the reaction channels. Suitable as a fluid are substances that can withstand temperatures up to about 350 ° C without decomposition, e.g. heat transfer oils such as Marlotherm, or molten salt, e.g. Na / K nitrites and / or Na / K nitrates. Heat removal by evaporative cooling, for example by water, is also possible.

The invention is illustrated by the following examples.

Example 1: Use of a plate reactor

40 mol / h hexaethylenediamine and 40 mol / h monochlorobenzene were mixed together, evaporated and preheated to 320 ° C. The resulting gas stream was mixed with 160 mol / h of gaseous phosgene, which was likewise preheated to a temperature of 320 ° C., in a mixing nozzle device consisting of a mixing chamber with two opposite inlets, with an entry speed of 80 m / s each on phosgene and Hexamethylene diamine / monochlorobenzene entry side. The gas mixture emerging from the mixing chamber was passed onto a rectangular duct with a width of 8 mm and a height of 62.8 mm and a length of 20 m. The channel was heated on both 62.8 mm wide sides to a temperature of 320 ° C with electric heating tapes. After leaving the channel, the hexamethylene diisocyanate (HDI) was selectively washed out of the reaction mixture in a known manner (see, for example, US 2,480,089) above the decomposition temperature of the associated carbamyl chloride with monochlorobenzene at a temperature of 165 ° C. The desired HDI was separated from the detergent monochlorobenzene by distillation in a yield of 98.5%. By applying a vacuum to the wash tower, an absolute pressure of 350 mbar was set in the wash tower and in the upstream reaction tubes. Pressure measurements were installed between the sewer and the mixing device as well as in the wash tower. At the beginning of the experiment, a pressure difference of approx. 79 mbar occurred between the pressure measuring points between the mixer and the duct and the pressure measuring point at the entrance to the wash tower, which corresponds approximately to the pressure loss in the flow due to friction in the pipe. After 24 hours of operation, there was still no sign of an increase in the pressure difference, which would be an indication of the narrowing of the free cross section due to the formation of solids in the pipe.

Comparative Example 2: Use of a tube reactor consisting of 10 parallel partial tubes, the total cross-sectional area of all tubes corresponding to the cross-sectional area between the two plates.

10

Analogously to Example 1, 40 mol / h hexamethylenediamine and 40 mol / h monochlorobenzene were mixed together, evaporated and preheated to 320.degree. The resulting gas stream was treated with 160 mol / h gaseous phosgene, which was also at a temperature of 320 ° C

15 was preheated, mixed in a mixing nozzle device consisting of a mixing chamber with two opposite inlets, with an inlet speed of 80 m / s each on the phosgene and hexamethylene diamine / monochlorobenzene inlet side. The gas mixture emerging from the mixing chamber was opened

20 10 parallel tubes with a circular diameter of 8 mm and a length of 20 m distributed. The tubes were heated to a temperature of 320 ° C. using electrical heating tapes. After exiting the tubes, the hexamethylene diisocyanate (HDI) became selective from the reaction mixture in a known manner

25 (see e.g. US 2,480,089) above the decomposition temperature of the associated carbamyl chloride with monochlorobenzene at a temperature of 165 ° C. The desired HDI was separated from the detergent monochlorobenzene by distillation in a yield of 98.5%. By applying a vacuum

30 the wash tower, an absolute pressure of 350 mbar was set in the wash tower and in the upstream reaction tubes. Pressure measurements were installed between the pipes and the mixing device as well as in the washing tower. At the beginning of the experiment, there was a pressure measuring point between the mixer and the reaction tube

35 and the pressure measuring point at the entrance to the wash tower a pressure difference of approx. 162 mbar, which corresponds approximately to the pressure loss of the flow due to friction in the pipe. After 24 hours of operation, the pressure difference in one of the pipes rose from 162 mbar to 187 mbar, which is an indication of the narrowing of the free cross section due to solid formation in the pipe. The attempt was then stopped.

5

Claims

claims

1. A process for the preparation of isocyanates by reacting primary amines with phosgene in the gas phase, characterized in that the reaction of amine and phosgene takes place in a reaction channel, the internal dimensions of the reaction channel having a ratio of width to height of at least 2: 1 ,

2. The method according to claim 1, characterized in that the reaction channel is a plate reactor, the internal dimensions of the plate reactor having a width to height ratio of at least 2: 1.

3. The method according to claim 1 or 2, characterized in that the inner dimensions of the reaction channel have a height of 1 millimeter to 50 centimeters.

4. The method according to any one of claims 1 to 3, characterized in that the length of the reaction channel is at least ten times the width of the reaction channel.

5. The method according to any one of claims 1 to 4, characterized in that toluenediamine, 1,6-diamino-hexane, l-amino-3, 3, 5-trimethyl-5-aminomethylcyclohexane or 4,4 'as the primary amine -Diaminodicyclohexylmethane, is used.

6. The method according to any one of claims 1 to 5, characterized in that the gaseous phosgene used by a

Distribution element at the beginning of the reaction channel is distributed over the entire width of the reaction channel and the gaseous amine is fed to the distributed phosgene stream.

7. The method according to any one of claims 2 to 6, characterized in that the reaction takes place in a reactor block containing two or more of the plate reactors described in claim 2.

8. The method according to claim 7, characterized in that the reactor block contains a fluid suitable for temperature control, which at least partially envelops the plate reactors.

Sign.

9. Use of a reaction channel according to one of claims 1 to 4 for the production of isocyanates by reacting primary amines with phosgene in the gas phase.

10. Use of a reactor block according to claim 7 or 8 for the production of isocyanates by reacting primary amines with phosgene in the gas phase.